This invention relates generally to gas turbine engines and, more particularly, to a fuel nozzle for a gas turbine engine.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial gas turbines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC & CO).
Accordingly, at least one known industrial gas turbine application includes a steam injection system that is configured to inject steam into the combustor to facilitate reducing nitrous oxide emissions from the gas turbine engine. However, when the steam injection system is not in use, i.e. during dry operation, at least one known gas turbine engine utilizes at least one of an air or fuel purge to reduce the potential for cross-talk between adjacent fuel nozzles and/or to reduce backflow into the fuel nozzle caused by off-board steam system leakage. Cross-talk as used herein is defined as the inflow through a first fuel nozzle and outflow through a second fuel nozzle caused by a circumferential pressure distribution within the combustor. More specifically, at least one known gas turbine engine includes a relatively large steam circuit flow area, such that compressor discharge bleed air supply is insufficient to purge the fuel nozzles. Similarly, utilizing gas to purge the fuel nozzle results in a relatively small purge flow, which is insufficient to provide protection against the aforementioned situations.